Democrats and many Republicans are pushing to preserve a pair of recently revived renewable tax credits in a potential comprehensive overhaul of the tax code, lawmakers told Bloomberg BNA.

An energy specialist, however, said those tax credits would have to be on the chopping block in a full overhaul. And Senate Majority Whip John Cornyn (R-Texas) told Bloomberg BNA all options are available to free up revenue offsets that would pave the way for a paid-for overhaul.

The situation involving the tax credits is among the many indications that overhauling the tax code will be an extremely formidable task. The 2.3-cent-per-kilowatt-hour wind production tax credit will begin a phaseout in 2017 with a 2020 expiration, while a 30 percent tax credit for the solar industry will phase out from 2020 through 2022.

Because of the policy certainty provided by the wind phaseout, according to the American Wind Energy Association, 8 gigawatts of wind power capacity are now under construction or in advanced development. And the roughly 27 gigawatts of solar energy cumulatively installed in the U.S. at the end of 2015 are expected to reach nearly 100 gigawatts by the end of 2020, the Solar Energy Industries Association says.